In the conventional art, in cooperation with a traditional three way switch, a ballast circuit of a fluorescent lamp can adjust the light output of the fluorescent lamp and provide three discrete levels of light intensity.
U.S. Pat. No. 5,821,699 discloses a three level dimming ballast for a fluorescent lamp. The U.S. patent adapts a bridge rectifier to obtain a first power level for the fluorescent lamp, adapts a double voltage rectifier to obtain a second power level for the fluorescent lamp, and adapts a double voltage rectifier and changes the operating frequency of the ballast to obtain a third power level for the fluorescent lamp.
However, for the first power level, the above described ballast may have a problem of startup under lower temperatures, low voltages and low power levels. Moreover, such a ballast is not suitable to use with a 230V Alternating Current (AC) input voltage.